The invention relates to a device for producing an undercut in a drill hole and including a drilling tool provided with a shank adapted to be received in a chuck of a drilling machine and having a convex collar supported on a corresponding concave bearing surface of a bearing element.
To produce an undercut in the drill hole, a drill bit with lateral cutting edges projecting at the drill bit head can be used. The undercut is produced by first of all inserting the drill bit as far as the bottom of the drill hole and then swivelling it in this position. In this process, in the region of the bottom of the drill hole the drill bit head reams out an undercut, into which an expansible plug with an expansible sleeve can be inserted with a matching fit.
Such drill holes with an undercut can be made even in facing panels or similar structures, but in these cases the undercuts have to be very accurate, so that upon insertion and expansion of an expansible anchor, the expansion pressure is not too great. Too great an expansion pressure may result in a part of the facing panel breaking away. To produce an accurate undercut, a drill bit with a diamond milling cutter can be used, but in the process of reaming out the undercut the function of the cutter is severely impaired by the accumulating stone dust.